1. Field of the Invention
The present invention relates generally to a novel method of manufacturing a novel multi-layer hollow article and, more particularly, to a method of manufacturing a hollow article having at least three layers of three kinds of resin or polymeric materials by the use of an extrusion molding technique and a blow molding technique.
2. Description of Prior Art
Conventionally, a hollow article composed of a resin material is generally formed through a blow molding process in which a pressurized gas is blown into a parison inserted into a set of molds. Sometimes a multi-layer parison having a plurality of resin layers laminated together has been employed in the blow molding process, the multi-layers complementing insufficient properties for a molded product of a single resin material.
In a fuel tank made of a resin material, such as high-density polyethylene, for example, a problem of gasoline permeation exists in which the gasoline stored within the tank tends to permeate through the tank wall. Japanese Patent Publication (Tokkosho) No. 55-39448 discloses a hollow article having a plurality of resin layers laminated together and formed from a parison by the use of a blow molding technique to deal with this problem. More specifically, the aforementioned multi-layer parison is formed using an extrusion molding process. The multi-layer parison has an inner barrier resin layer composed of a sub resin, such as a nylon resin, for preventing the gasoline from permeating through the tank wall, an outer resin layer composed of a chief resin, such as a high-density polyethylene, and an intermediate adhesive resin layer. The adhesive resin layer is formed between the inner barrier resin layer and the outer resin layer and securely bonds the inner barrier resin layer to the outer resin layer. Accordingly, the hollow article is formed from the parison by the use of a known blow molding technique and has three resin layers of three different kinds of resin materials.
When making such a hollow article by the use of a blow molding technique, an outer portion of the parison is jutted out or projected from the cavity of the blow mold toward the outside of the blow mold creating a flash. Thereafter, when the parison becomes hard, this flash must be removed. It is desired that the flash be recycled for a cost savings and effective use of material. However, the flash of the hollow article includes both the nylon sub resin material as well as the polyethylene chief resin material. The nylon resin is of low heat stability and is not related chemically to the high-density polyethylene. Thus, the articles formed by the use of the recycled resin material experience problems due to low mechanical strength and opaqueness. As a consequence, generally the flash is not recycled.